Determination of Residues of 53 Common Pesticides in American Ginseng by Gas Chromatography-Tandem Mass Spectrometry Combined with QuEChERS

About 2 g of American ginseng powder was taken, and 10 mL of 1% (volume fraction) glacial acetic acid solution was added. The mixture was homogenized for 5 min, and 10 mL of acetonitrile-toluene mixed solution at volume ratio of 3∶1, and 1 mL of mixed internal standards (consisting of triphenyl phosphate, parathion-d₆ and atrazine-d₅) stock solution were added. The mixture was shaken for 1 min, and 7.5 g of mixed powder composed of anhydrous magnesium sulfate and anhydrous sodium acetate at mass ratio of 4∶1 was added. The mixture was shaken for 3 min, cooled in ice water bath for 10 min, and centrifuged for 5 min. An aliquot (9 mL) of the supernatant was taken and placed into a purification tube containg 900 mg of anhydrous magnesium sulfate, 300 mg of PSA, 300 mg of C₁₈, 300 mg of silica gel and 45 mg of GCB, and the mixture was vortexed for 1 min, shaken for 5 min, and centrifuged for 1 min. The supernatant was passed through a 0.22 μm filter membrane, and 1 mL of the continued filtrate was taken, and mixed with 0.3 mL of analyte protectant solution composed of D-(+)-riboacid-1,4-lactone and sorbitol. The mixed solution was made its volume up to 2 mL by acetonitrile, which was introduced into gas chromatograph-triple quadrupole mass spectrometer for analysis. The targets were separated on SH-Rxi-5Sil MS column under temperature programmed conditions, ionized by electron impact ion source, detected by multiple reaction monitoring mode, and quantified by matrix matching method combined with internal standard method. As shown by the results, the same linear range of working curves of 53 pesticides was 2.5-200 μg·L^-1, with detection limits (3S/N) in the range of 0.001-0.002 mg·kg^-1. Test for recovery was made according to standard addition method, giving results in the range of 69.1%-107%, and RSDs (n=6) of the determined values were less than 10%. The proposed method was applied to the analysis of 50 batches of imported American ginseng samples, and 1,1-bis(4-chlorophenyl)-2,2-dichloroethylene, 2,4'-dichlorodiphenyltrichloroethane,1,1-dichloro-2,2-bis(4-chlorophenyl)-ethane, 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane and pentachloronitrobenzene were detected, and the overall risk of pesticide pollution in American ginseng was controllable.